While Windows Vista may be Mr. Ballmer's greatest disappointment, the driving force behind his departure was arguably Windows 8.

Windows 8 started off a promising concept, but fell victim to a myriad of flaws and shortcomings, which have led to the biggest percentage drop in PC sales ever. One major issue was the scope of the redesign -- Microsoft dropped a very new and different interface on consumers with the graphically rich "Modern UI" (aka Metro) homepage and a slew of new multi-touch gestures. Where other similarly complex OSs such as Android include a built-in tutorial that helps teach users how to use the new UI, Windows 8 had no such tutorial. As a result many customers wrote Windows 8 off quickly, "downgrading" to Windows 7.

Even as Mr. Ballmer prepares his exit, his company is aiming to fix some of its Windows 8 misses with Windows 8.1.

The Start Button hovers in Windows 8.1 allowing a fast return to the Desktop Mode. New users are now greeted with tutorials to help them learn the foreign interface in more of a friendly fashion. [Image Source: CNET]

It also integrates numerous other improvements, including unified themes; new Modern UI core apps; the ability to unpin, group move, and resize tiles at will; and an improved Windows Store.

Microsoft has taken a gamble by putting the people behind Windows 8 and its mobile twin Windows Phone 8 in key positions of leadership, during the recent executive shakeup. This is a clear testimony to the fact that while Mr. Ballmer may be being shuffled out the door, Microsoft's Board of Directors believes the company was headed in the right direction with Windows 8 and merely failed on the delivery.

Windows 7, Microsoft's greatest sales success, was born out of the ashes of the poorly received Windows Vista. Likewise Microsoft is looking to hone the sooty carbon of Windows 8 into a diamond with Windows 8.1. Windows 8.1 RTM is the last major milestone in that pre-release refinement process.